1. Field of the Invention
The present invention relates to an image processing method and an image processing apparatus for creating synthetic image information by embedding other additional sub-information (such as security information) in an invisible state in main image information (such as a face image of a person) in a visible state for synthesis and restoring the sub-information from the synthetic image information.
2. Description of the Related Art
In recent years, with electronization of information and widespread use of the Internet, greater importance is being placed on technologies such as electronic watermarking and electronic signature to prevent forgery or falsification of images. Particularly, the electronic watermarking technology that embeds additional sub-information (such as security information) in an invisible state in main image information (such as a face image of a person) is used as countermeasures against illegal copying, forgery, and alteration of ID cards and photos in which copyright information is embedded.
For example, Japanese Patent No. 3547892 (Patent Document 1) describes an electronic watermarking insertion method of embedding data in image data to be output to printed matter by utilizing characteristics of high spatial frequency components and color difference components that are more difficult for humans to perceive. However, it is basically difficult to apply the method described in Patent Document 1 to binary images (for example, black and white binary images) such as documents.
Also, “Data Embedding in Binary Images by Block Error Diffusion Method”, Makoto Nakashizu (Tokyo University of Agriculture and Technology) et al., Journal of IIEEJ (The Institute of Image Electronics Engineers of Japan), Vol. 31, No. 4 (2002)” (Patent Document 2) describes a technique to embed electronic watermarking in binary images by using the error diffusion method in blocks. However, Patent Document 2 describes only evaluation in a state of digital data before printing. That is, Patent Document 2 is not intended for printed images even if the error diffusion method is used. Further, Patent Document 2 does not describe any method of restoring electronic watermarking.